1. Field of Invention
Embodiments exemplarily described herein relate to a fuse box and associated methods of cutting a fuse within a fuse box.
2. Description of the Related Art
Generally, during the fabrication of memory devices, when there is even one defective cell, a memory device cannot perform its function and is treated as a defective product. Accordingly, redundant cells are formed to replace the defective cell in order to improve throughput. Conventionally, spare rows and columns of redundancy cell are formed to replace defective cells in row and column. Specifically, after forming a memory device on a wafer level, a test is conducted to find defective memory cells and a program is run in an inner circuit to replace the addresses of the detected defective cells with the address signals of the spare cells. Accordingly, during actual use of the memory device when the address signals corresponding to the defective lines are inputted, the redundant cells are selected to replace the defective lines. One method of this program is to use a laser beam to blow and cut a fuse. The wiring that is disconnected by the laser beam emission is called a fuse line, and the region around the fuse line is called a fuse box.
Referring to FIGS. 1 through 5, a conventional fuse box and a conventional fuse cutting method using the fuse box will be described. The structure of the conventional fuse box is shown in FIGS. 1 and 2. FIG. 1 is a top plan view of a conventional fuse box, and FIG. 2 is a sectional view taken along line I-I′ of FIG. 1. Referring to FIGS. 1 and 2, a first interlayer insulating layer 2 is disposed on a substrate 1. Metal wirings 3a and 3b are disposed on the first interlayer insulating layer 2 and the substrate 1. A second interlayer insulating layer 5 is disposed on the metal wirings 3a and 3b and the substrate 1 and fuse lines 9 are disposed on the second interlayer insulating layer 5. Each fuse line 9 is connected electrically to the metal wirings 3a and 3b through contact plugs 7a and 7b passing through the second interlayer insulating layer 5. A third interlayer insulating layer 11 and a passivation layer 13 are disposed on the fuse lines 9 and the second interlayer insulating layer 5. A fuse window 15 is defined within the passivation layer 13. The fuse window 15 exposes the fuse region of the fuse lines 9, and traverses the fuse lines 9. The fuse window 15 is formed to cut the fuse lines 9, and its width W1 is narrower than the length L of the fuse lines 9. Thus, in a conventional fuse box, the contact plugs 7a and 7b connected to the fuse lines 9 are not exposed through the fuse window 15, as shown in FIGS. 1 and 2. The problems that can arise in this conventionally-structured fuse box will now be described with reference to FIG. 3.
FIG. 3 is a sectional view showing fuse lines 9 cut with a laser beam 17 passing through a fuse window 15. Referring to FIG. 3, when a fuse line 9 is cut by the laser beam 17, cut portions 99 remain at the edges of the fuse window 15. The cut portions 99 of the fuse line 9 corrode when exposed to moisture in the air so that the volumes of the cut portions 99 expand. The expanding force is exerted vertically so that the third interlayer insulating layer 11, the passivation layer 13, or the second interlayer insulating layer 5 develops cracks {circle around (a)}. The cracks act as moisture passages {circle around (1)} that accelerate absorption of moisture, which can adversely affect a device formed on the substrate 1 (e.g., a main memory device) in a drastic manner. Also, the cut portions 99, the contact plug 7a and 7b, and the metal wiring 3a and 3b of the fuse box structure provide two other second moisture passages {circle around (2)} passing therethrough. Additionally, when corroded, the cut portions 99 can become electrically connected with the adjacent fuse lines 9. Also in the above conventional fuse box, only one fuse region of the fuse lines 9 is exposed to the laser beam 17 through the fuse window. As a result, cutting defects can easily occur during actual manufacturing. This type of defect will be described further with reference to FIG. 5.
FIG. 4 is a sectional view of an exemplary conventional structure for preventing corrosion caused by moisture absorption and cracking. The width W2 of the fuse window 15 in this structure is greater than the length L of the fuse lines 9. Thus, the fuse lines 9 are completely exposed through the fuse window 15, whereby the passivation layer 13 is not disposed above the outer edge portion of the fuse lines 9. Accordingly, after the fuse line 9 is cut, even when corrosion occurs, the expanding caused by the corrosion is directed outward due to the lack of the passivation layer 13 thereon, thus reducing the occurrence of cracks.
However, as shown in FIG. 5, at least two moisture passages {circle around (3)}, similar to the moisture passages {circle around (2)} shown in FIG. 3, are formed during fuse cutting and a cutting defect {circle around (b)} is generated. In particular, when the energy of the laser beam 17 for cutting the long fuse line 9 is applied too intensely, damage can be inflicted to the device itself. Because adequately adjusting the intensity of the beam is difficult, cutting defects can easily occur.